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Longer Runners


I was thinking of getting some silicone hose to make new couplers for the intake.
I wonder if I added an inch or so if there would be any benefit or not?
Paul Nimz

I would be concerned about the main connection into the expansion chamber. It really isn't a straight line in as I recall.
Carter Fuji 
I don't understand??
**Now that's a first - U.L.**
IIRC the original Porsche designed Duratec 2.5l utilized a runner length that positioned the surge tanks to the outboard edge of the valve covers . Possibly how the lil 2.5 was output at over 250 hp . Detuned of course by Ford .....sounds kinda familiar don't it ? I'd say go for it - You Will have to tune for it of course coupled with the Fandango exhaust you posted may show some improvements through the rpm range.
Rick B
I'll have to do more beersearch on it. but I will have more hose than what I need. So...
**AttaBoy - Beeresearch!!! How Ford developed cam sprockets!**
The 8 runners would extend out no probably the big one from the curved tube out of the throttle body is at a slight angle, not an easy connection if you make the distance further?
Carter Fuji 
I would have to I guess. It would still be a straight connector. 3.5" IIRC. The runners are 2"
Gotta' love beer engineering...
Carter Fuji

Engibeering? Okay, maybe not... Sorry.

Jon Heese
we used to call it thinking sessions..
problem was more beering then engineering was done.
wonder we ever got anything done.

Clare * I can't use the shift key to save my cdn hockey playing arse**
Longer runners will lower the resonant frequency of the intake . If you look at the volumetric efficientcy (VI), the VI peaks occur at harmonics of the resonant freqency of the intake.

I didn't feel like typing it all out myself, so I'm borrowing this from www.rogueperformance.com. Thanks Fred.

L = ((ECD 0.25 V 2) (rpm RV)) - D

To compute the intake runner length (L), we need to know a few things:
-Effective Cam Duration (ECD) = 720 (4 cycle engine) - Advertised Cam Duration (Factory ~248 ) - 20 (lifter slop)
-Runner Diameter (D) = 1.5 (or so)
-Speed of Sound (V) = 1250 to 1300 fps,depending on temperature (use 1300)
-Reflective Value (RV) = How many times is the air going to bounce before the intake valve opens? Use 2 for LONG runners with high RPM's or 4 for short runners with moderate RPM's.
-Revolutions Per Minute (rpm) = 2500 for a good street intake, low RPM, daily driver or tow.

Use the stock length (if you know it) and find the resonant RPMs, then repeat with an added inch and see how it changes.

Daniel J Holtman
Olivet Nazarene University
Department of Engineering

**I knew an engineer once, said it was a tough gig following those darn tracks!!**
Just sitting here and playing with the equation using dummy numbers,
it looks like about one inch change in runner length will result in
the VI peak moving around by roughly 400-500 rpms (longer runners =
lower rpm for VI peak). That's just a stab in the dark, really. I
assumed runner lengths of 8" and 9".

It's early, though, and I'm only on my second cup of silver needle. I
could be way off...

What is the difference in runner length on the primaries and
secondaries of the V6 SHO engine? We can bounce that number off the
peak HP numbers on the numerous dyno graphs that are around and make
some more inferences.
|Dan Carman
The Little Brass Colored Runners Inside the Surgetank are ~3" avg.
(The round ones are longer)
Then about 9" for the Upper Runners.
Then 2" for the IMR set.
Then about 2 more Inches in the Heads.

Try 16" for a fairly close stab in the Dark

Eric in Memphis :-)

P.S. - Gonna be 104' F today. Just Stupid Hot.

P.P.S. Beale Street was Hands Down the COOLEST SHO Gathering I've Ever
Seen or Been a Part of. SHO Parking ONLY.

Eric Lehmann
That's just a stab in the dark, really. I assumed runner lengths of 8" and 9".
Dan Carman
Yeah, I forgot about all the crap you can't see until you open everything up.

Well in that case I'm getting a change of about 150-200 rpm per inch
change in runner length. Sounds like a waste of time, but I could be
screwing something up in the calculations (I'm awake now, but I'm

I'm also curious about what effect the surge tank has on resonance.
THAT would be a real pain to calculate.
Dan Carman

Just a reminder: you can move peak HP up and down. But you can not MAKE HP.
It is a zero sum game. Where ever you move HP from HP will be less.

Also I think the runner length is ambiguous by design to give a broad peak
not a sawtooth peak. Which is best with an ATX.
Tim "Buford" Wright
I had computed this some time ago for my V6, and found it was set at a good compromise. By increasing the length of the runners, the peak will move downward slightly, but causing a larger dip at the crossover point (when the secondaries open) than there is already. Additionally the 'Q' will decrease (electronics types will get this analogy) causing the effect to be less overall. Again this was for the V6 so YMMV re: the V8.

Mike Thompson
Well, that is only partially correct assuming that the current intake (on
any engine) is optimized as is. Changing the intake runner lengths,
diameters and type will indeed move HP around (up or down), but it can also
MAKE HP as well (as well as lose HP if done wrong). Now, that's not to say
that even though intake A makes 15 more HP than intake B that it will result
in the car running 'better' on the track. You also have to take power under
the curve into consideration as you alluded to with the 'broad peak'
statement you made.

It is conceivable that an intake could be designed for the V8 that makes
less PEAK HP but actually results in the car performing better at a 1/4 mile
track. All it would take is an intake that has better power under the curve
throughout the operating range the engine would see during the 1/4 mile

Dave Garber
At Gingerman I seem to be near the peak rpm in 2nd or into third. I would need to get the peak torque down a little IMHO.

Chasing Hirinsin around we were shifting at the same time. But he could not pull on me, nor me him. Not bad for a Gen 3 I guess.


**Both you dudes were lucky I wasn't there!!! (tee hee)*U.L.
I'm not too clear on what you're telling me - are you saying that when you are in second or third your RPM's are too low and away from the power peak? If so, then I see where you're going with this and yes, lengthening the runners will bring the power peak down in the revs closer to where your engine lives at Gingerman. The effect would be that you'd have more power at those engine speeds with the longer runners vs the stock lengths.

OTOH, if you are saying that you are near the rev-limit (7k rpms) in these gears, then lengthening the runners would exasperate the problem as it would further choke the engine at those engine speeds. And I don't know that you'd be able to lower the power peak enough to allow you to gear-up (from second to third or third to fourth) and be making any good power?

Dave Garber

BTW: If you're able to hang with Hrinsin's 3.4 V6, then you are doing great! His stroker V6 runs darn strong!

Be aware I have no secondaries. Kicked them to the curb for good a while back.


**Not entirely true!! I have seen the pile o parts in Pauls garage - they are nowhere near the curb!! Rumor has it Recycling guy would not take the pile!!** U.L.
The only thing I feel the V8 intake is optimized for is to fit. 

I remember once leaving the runner extensions out one time. Car ran like it had the secondaries stuck shut. Couldn't wait to put them back in.

So they are maybe an 1.5-2". Another 1" or so is what I am looking at maybe by way of the couplers.
Found all the silicone. Anybody need some new runner couplers?
They in Yellow or Bright Blue?
Carter Fuji
The guy has different colors. I would be getting black.
Is there any room to make longer extensions that go farther into the surge tank?
Dan Carman
You mean hang with Johns car with someone else driving it?? J with him driving it its not to hard to hang, wave and fill his car with exhaust!! 
Kirk J Doucette
Well I meant hang with him in the straights. :) The mighty stroked V6 Yamaha!

*Ed Note: Once it got to the equations, I got a headache. However, this thread took longer to edit than any other I can remember in the last 4 years. Still it's here cuz there is some good info and great smak all rolled into one. U.L.**

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